I emailed the question to the paper coauthor Michael Hudson, and
he replied:

In a nutshell, the filaments, like the rest of the Universe will
still expand indefinitely in the current picture.

The event horizon is analogous to a horizon on Earth, I.e. It is a
distance to which light can travel. It is not a physical force that,
for example, tears anything apart or generates some kind of tangible
barrier.

Mike Hudson, Professor
Dept. of Physics & Astronomy
University of Waterloo
Waterloo, ON N2L 3G1 Canada


[[Mod. note -- Ted Bunn's "Black Holes FAQ" is an excellent reference
to learn more about event horizons:
http://cfpa.berkeley.edu/Education/BHfaq.html
-- jt]]